1. Field of the Invention
The invention relates generally to semiconductor devices and, more particularly, to a method of forming a metal line of a semiconductor device, in which the volume fraction of the metal line can be maximized and the grain size of the metal layer can be increased, thereby improving the sheet resistance Rs of the metal line.
2. Related Technology
In general, a metal line of a semiconductor device is formed by means of a damascene scheme.
A process of forming the metal line of the semiconductor device using the damascene scheme is briefly described as follows.
An interlayer insulating layer is first deposited on a semiconductor substrate in which selected structures, such as a gate, are formed. Trenches are then formed, and a barrier metal layer of Ti/TiN is formed over the interlayer insulating layer including the trenches. A tungsten layer is formed over the barrier metal layer in such a way to gap-fill the trenches. Selected regions of the tungsten layer and the Ti/TiN barrier metal layer are etched to form a tungsten metal line.
As semiconductors products have become miniaturized and more highly integrated, the pitch of the metal line has decreased in size. Accordingly, when the metal line is formed by a general damascene structure in devices of 70 nm and 60 nm, the following problems are generated.
Firstly, in the case where a metal line is formed by a single damascene structure, the volume of a tungsten layer is decreased by means of a region occupied by a barrier metal layer within the trenches. Accordingly, a problem occurs since the resistance of the metal line increases.
Secondly, in the case where tungsten is deposited on an insulating layer, a lifting phenomenon is generated between the insulating layer and tungsten due to an adhesion problem. In order to prevent the problem, titanium (Ti) and titanium nitride (TiN) are laminated between the insulating layer and tungsten. However, when a tungsten nucleus is generated on the TiN layer, a large number of nuclei are created. Thus, the grain growth is rapid, but the grain size is decreased, resulting in an increased sheet resistance Rs.
Thirdly, in the case where a metal line is formed using a dual damascene structure, reduction of the target thickness of a barrier metal layer is limited due to junction resistance when the thickness of the barrier metal layer is reduced.
Attempts have been made to secure the resistance of the metal line by reducing the thickness of the barrier metal layer in order to solve the conventional problems. However, a reduction in the thickness of the barrier metal layer has reached a limit at 60 nm or less. Another attempt was made to improve the resistance characteristic of the metal line by minimizing a nucleus creation target of tungsten with a high resistivity. However, a reduction in tungsten nucleus creation has reached limitation at 60 nm or less.